The present invention relates to target-seeking missiles and, in particular, it concerns a miniature target-seeking missile for attacking surface targets, and corresponding methods of operation of a missile.
Various types of target-seeking missiles have been developed to address differing operational needs in modern warfare, each characterized by particular combinations of features. In general, missiles for targeting aircraft (i.e., air-to-air missiles and surface-to-air missiles) require extremely high speeds, typically in the range of 3-4 mach, in order to close in upon a fast-moving target. Particularly in the case of air-to-air missiles, high seeker gimbal angles and high maneuverability are also required in order to facilitate targeting of an enemy aircraft which is at a high angle off boresight. In order to maintain aerodynamic stability under these extreme operating conditions, some of the most recent generations of air-to-air missiles employ three or more independently controlled sets of symmetrically deployed aerodynamic control surfaces, particularly to allow independent management of the sensitive roll control-loop of the missile in flight. Thermal imaging seekers typically cover wide angles approaching full hemispherical coverage. The missiles are typically large, often with a pre-launch weight in the region of 100 kg.
Guided missiles for targeting surface targets (i.e., air-to-surface and surface-to-surface missiles) are configured for very different operating conditions, and therefore differ greatly from air-to-air missiles. For example, missiles for targeting surface targets typically do not require such high speeds, and are typically subsonic or at most around the speed of sound. Many guided missiles provide capabilities for following progress of the missile in flight and correcting, or even changing, the target during flight. Particularly in such cases, relatively slow speeds are preferred to allow time for controlling the missile. The combination of lower speeds, lower maneuverability and often relatively high weight avoid many of the problems of aerodynamic control, particularly of the roll parameter, present in air-to-air missiles. As a result, missiles for surface targets commonly employ a set of four fins for controlling pitch, yaw and roll.
A further distinction between missiles for surface targets and those for airborne targets is the range of seeker gimbal angles required. Surface-to-surface missiles and air-to-surface missiles typically home-in towards a target which is itself stationary or relatively slow moving. This ensures that the target is always more-or-less ahead of the missile, thereby allowing the use of imaging seekers with relatively small gimbal deflection angles, such as about ±30°.
At the small end of the scale of surface-to-surface guided missiles are man-portable or man-packable missiles which try to bring the capabilities of precision attack weapons to the infantry arena. Shoulder-launched anti-tank missiles are already well established, but their high price tag (typically in excess of US $40,000) limits their use to high-value or strategic targets. In order to provide a lower-cost option which would be suitable for lower-value “soft” targets, attempts have been made to scale-down and simplify missiles along the same conceptual lines as the anti-tank missiles to provide a miniature guided missile for mass production as an infantry weapon.
One recent example of these attempts is described in U.S. Pat. No. 6,244,535 to Felix. Felix describes a low cost miniature missile for use against low-value “soft” targets. The missile is described as having a weight of about 2 kg, length of about 46 cm, and body diameter of about 4 cm. It is driven by a low-speed rocket motor and employs 3 or 4 canards for aerodynamic control which are said to generate lateral accelerations of up to between 4 G and 8 G at 220 m/s. The missile implements a reduced performance navigation law based on a “simplified” guidance system. For target tracking, the missile employs a fixed (non-gimbaled) imaging sensor with a frame rate below 15 Hz in order to reduce costs and simplify processing. The fixed imaging sensor requires use of a non-optimal flat fly-out trajectory in order to avoid losing the target from the edge of the field of view. The missile operates in a “fire-and-forget” modality with inferior (“simplified”) tracking algorithms based on two-dimensional edge detection algorithms only.
For short range targets, situations frequently arise where the location of a desired target is well known but the target is obscured from view from the launching position. The missile of Felix, limited to “fire-and-forget” modality, clearly cannot be used against obscured targets. Furthermore, the flat fly-out trajectory of the Felix missile results in a line of sight close to the ground which is susceptible to momentary disruption by intervening objects during flight, thereby risking target tracking failure.
For longer ranges, it is known to use anti-tank missiles to attack a target which is obscured from direct view of the launch location. Such situations are typically classified in the art as “BLOS” (“beyond the line of sight”) for situations where the target is immediately behind a visible cover or “NLOS” (“no line of sight”) for situations where some intervening object (e.g., a hill or building) obscures the region of the target. In either case, the target can be attacked by launching a missile along an elevated flight path until the obscuring obstacle no longer obstructs view of the target and then locking-on to the target. In a BLOS scenario, the missile is typically initially locked-on to the cover or another object adjacent to the target and then the target is updated (“fire-and-update”) when the target comes into view. For NLOS scenarios, the missile is typically launched along an initial flight path under inertial guidance and locks on to the target during flight (LOAL-“lock-on-after-launch”). For shorter ranges, however, existing surface-to-surface missiles lack sufficient maneuverability to start along a high flight path and still bend the flight path down sharply enough to reach the target. The problem becomes even more pronounced where a target is located immediately behind a shielding structure such as a wall or building so that it may not become clearly visible until the missile is almost overhead. Additionally, in the modern warfare arena, there is a growing need for pinpoint attack capabilities which can target terrorists or other specific localized threats located within a civilian environment with the minimum possible collateral damage.
There is therefore a need for a small guided missile which would provide an effective solution for short range obscured targets, and which would allow pinpoint targeting of small targets with reduced collateral damage.